The possibility of using electron beams to pump a laser, either directly or secondarily through a photolytic process, is an attractive spectre, offering far higher efficiences (typically, 4-10%) than conventional flashlamp pumping. If one would use an electron beam to repetitively pump a laser oscillator or amplifier, directly or indirectly, the electron beam device must supply a multiplicity of short electron beam pulses (each pulse being nanoseconds to microseconds in length) at moderate interpulse microseconds or longer).
Akimov, et al, 1 Journal of Quantum Electronics 649 (English translation) (1972) indicates the use of an electron beam with repetition rate of 250 Hz, to drive a semiconductor laser, but no details are given.
Yamamoto, et al, 45 Journal of Scientific Instruments 591 (1974) teach the use of additive combinations of positive and negative voltage pulses propagating in a transmission line to achieve short e-beam pulses (.DELTA..tau..about. nano-seconds) with repetition rates of 1-1000 Hz. The currents are small here, being less than 1 amp.
Babaev, et al, 4 Soviet Journal of Quantum Electronics 777 (English translation) (1974) describe an electron gun which produces large currents (.about.500 amps) at repetition rates of 5 Hz with pulse length 1 .mu.sec. apparently using conventional approaches to e-beam formation.
Ault, 26 Applied Physics Letters 619 (1975) discloses a high current density (J.gtorsim.100 amps/cm.sup.2), low impedance transmission line electron pulser allowing repetition rates of 1 Hz. The device uses a sequence of six cathode blades, radially directed on a cylindrical or coaxial geometry.
Loda and Meskan, "Repetitively Pulsed Electron Beam Generator", Electron Beam Technology Symposium, Sandia Corporation (Albuquerque, New Mexico, Nov. 1-3, 1975) discuss a long pulse length (.DELTA.t.about.3 .mu.sec) electron beam generator with current density J.about.1 amp/cm.sup.2, having a repetition rate of 50 Hz and a large useful aperture (area.about.1 (meter).sup.2). Cold emission from a tantalum foil cathode is used to generate a timed series of emissions at different points along the foil, although it is unclear how controllable is the time sequence of emissions.
Weinfeld and Bouchoule, 47 Review of Scientific Instruments 412 (1976) disclose a short pulse (.DELTA.t.ltorsim.1 nsec), low energy (1-100 eV) electron gun having a repetition rate of perhaps 100 MHz, using a step recovery diode which manifests alternate low and high impedance states, depending upon the rapidly changing bias applied at the diode. The energy and current density of an assembly of such diodes are apparently limited to low values.
U.S. Pat. No. 3,925,670 to Farrell, et al teaches the use of a rapidly pulsed cold cathode system to obtain repetition rates of 1-10 kHz with slow rise time (.gtorsim.0.1 .mu.sec) and relatively long pulse lengths (0.1-10 .mu.sec). The electrons thus produced tend to spray over a large area, which may make attainment of beam uniformity a problem.
U.S. Pat. No. 3,956,711 to Waynant discloses a travelling wave transverse electron beam using timed electron emission from a sequence of thin blades driven seriatim by a high voltage transmission line. The time sequence for firing is controlled by cutting different lengths for each of the cables connecting blades and line so that in principle arbitrary pulse repetition rates are possible. However, the cathode spatial emission is non-uniform by definition; and the emission current density associated with any one blade is small as it represents a fraction of the current initiated by a single pulse from a capacitor bank.
Only in Weinfeld, et al has a 10.sup.4 Hz repetition rate been exceeded and that was for short pulses of pulse length less than 1 nsec and low energy (1-100 ev). The electron gun to produce a higher repetition rate at higher energies is lacking in the art shown above. Such a requirement is necessary for repetitively pulsed regenerative amplifiers in order to excite the lasing medium before each laser pulse passage.